However, the phase boundary isn't as sharp as for a pure molecule. Paraffin is a collection of linear hydrocarbons of various lengths, and the melting point, as a consequence, is quite broad (and a little bit higher than 37°, or it would melt in your hand). Its lubricating properties are probably a consequence of the indistinct phase boundary. It is a little bit like a crystal of a biological macromolecule, which is in many ways more like a highly concentrated solution that happens to be ordered in a three-dimensional array. I don't want to push that analogy too far, because paraffin crystals (which are formed during purification) are macromolecular crystals without any other solvent present. Because they are hydrocarbons, they form no electrostatic or hydrogen bond interactions, so the crystals themselves have very little structural integrity, and, again, there is a mixture of molecular weights. So waxes, and wax-like substances like polyethylene glycol, have broad, indistinct phase boundaries. Another way to see that is their diffraction properties. We used wax rings to align X-ray detectors and the beam prior to data collection; (it makes it much easier to index a diffraction pattern). The rings (which are like a powder pattern) correspond to the correlation lengths of carbon atoms between molecules, and are a standard way of characterizing phases (and identifying phase changes) for condensed-matter chemists. For wax, unlike most solids, there is no abrupt transition upon melting. I rather suspect this again is a feature that makes it a good lubricant.